DE2722972A1 - NITROGEN CONTAINING POWDER METALLURGY TOOL STEEL - Google Patents

Description

Applicant: Kobe Steel, Ltd.

3-18, 1-Chome, Wakinohama-cho, Pukiai-ku Kobe / Japan

Powder metallurgy tool steel containing nitrogen

The invention relates to a tool steel; in particular, it relates to a nitrogen-containing powder metallurgy steel (hereinafter referred to as "PM steel"), its contents at C, N and V are suitably matched to one another.

It is known that the properties of tool steels containing alloy elements such as Cr, W and V are improved can be achieved by incorporating nitrogen into the steels (cf. e.g. "Kobe Steel Technical Bulletin", R & D, Volume 24, No. 3, Pages 11 to 15, and Japanese Patent Laid-Open No. 78 606/74, 49 109/75 and 49 156/75), and these steels are used to a large extent as collecting materials, for example as embossing or drawing materials and as cutting tool materials are used because they have good wear resistance and good heat resistance. By a Nitriding treatment is a nitride of type MX or MgX (wherein M stands for an alloy element and X stands for carbon or nitrogen) and this nitride is more stable as an MC or MgC type carbide. Accordingly, will the appropriate quenching temperature range is broadened and ν

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the control of the heat treatment can thereby be facilitated. In addition, the temper hardening properties are improved and a fine austenitic crystal structure can be obtained to improve mechanical properties. Furthermore, the loading or. Processability can be improved.

According to Japanese Patent Publication No. 19 77VW, the addition of 0.05 to 0.35 % N to a die steel for use at high temperature contributes to an increase in resistance to softening at high temperature, it suppresses greasiness *) of grain boundaries and also contributes to suppressing excessive 6-ferrite formation.

Most conventional nitrogen-containing tool steels have hitherto been manufactured using the melting process. When the fusion process to manufacture of 7 / tool steels containing nitrogen is used, Complicated steps must be carried out, for example the steel must be in a high pressure nitrogen atmosphere be melted, or a nitride must be incorporated into the molten steel. Because the amount of in that Nitrogen contained in steel is low and because it is difficult to form a fine carbonitride and make it evenly within To distribute the steel, it is also in the melting process impossible to improve the properties to the desired values.

Recently, as a way of overcoming the disadvantages or limitations encountered in the melting process, there have been processes for the production of nitrogen-containing tool steels by the powder metallurgy process or by the Puiyerschmiedeververfahren proposed. In these procedures can be made by taking advantage of the fact that dna powder is a great

* (fatting)

> 0 9 8 4 7/1 1 7 ^r =

has a specific surface (surface size / volume), and the fact that a powder sintered body has a porous structure, in a simple manner, for example by prior addition of nitrogen to the starting powder or by adjusting the heating temperature, the heating time or the nitrogen partial pressure in the treatment atmosphere in the sintering stage, any amount of nitrogen be introduced into the steel. It was to be assumed that in these processes the nitrogen was fine within the steels and distributed evenly.

In the conventional PM steels containing nitrogen however, the machinability is not improved as much as would have been expected from the Japanese Patent Publication No. 37 810/1972 emerges. N is not an advantageous element for stabilizing the retained austenite when the steel is to be used as a gauge (see e.g. Japanese Patent Publication No. 9900/1972). The machinability is rather worsened by the incorporation of nitrogen into the steels. It therefore becomes frequent take the view that the value of the nitrogen-containing high speed steels (high speed steels), which after the Powder metallurgy processes have been produced is questionable. However, some high-speed PM steels containing nitrogen have which have recently been used in practice, a good machinability or processability in combination with a shown good wear resistance. The reason for this is not yet known. In particular, there is no clarity on the relationship between the amounts of alloying elements that give the steel excellent machinability confer, and the amount of nitrogen enrichment. Therefore, the types of steels are subject to being enriched with nitrogen are, for the manufacture of cutting PM steels and that can be used, drastic limitations.

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For example, it is stated in "Kobe Steel Technical Bulletin", R + D, Volume 24, No. 3, Page 10 that when high-speed PM steels of the Mo type (JIS SKH 9 and modified JIS SKH 55) 0.4 to 0.5 % N is added, the workability is significantly improved.

Taking into account the fact that the addition of N is very beneficial for a fine and uniform carbide Research work has now been carried out with the aim of finding various properties that are required for a tool steel I, especially the wear resistance and the impact resistance or the impact resistance, with regard to various steel compositions. After extensive research finally became the tool steel according to the invention found.

It is an object of the invention to overcome the problems encountered with conventional HI tool steels containing nitrogen to solve. The main object of the invention is to provide nitrogen-containing PM tool steels with excellent wear resistance and excellent impact properties or an excellent notched impact strength. These and other goals of the invention can be achieved by the features of the invention, which are described below with reference to the attached drawings are described in more detail. Show it:

Fig. 1 is a graph showing the relationship between the nitrogen content and the properties of about 0.5% Shows JIS SKH 9 steels containing C;

Fig. 2 is a graph showing the relationship between (C + N) content and properties of 0.1 to 0.7 % C-containing JIS SKH 9 steels;

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Fig. 3 is a graph showing the relationship between (C + N) content and properties of steels containing 0.3 to 0.9% C;

Fig. 4- is a graph showing the relationship between (C + N) content and properties of steels containing 1.7 to 2.5% C;

Fig. 5 is a diagram showing the relationship between the

Shows (C + N) content and properties of 0.2-0.9 % C-containing steels;

Fig. 6a is a photograph showing the microstructure of the steel ⁰ manufactured by the powder metallurgy method; and

Fig. 6b is a photograph showing the microstructure of the steel made by the melting process.

High-speed steels (high-speed steels) are characterized by their excellent wear resistance and their excellent Heat resistance because they contain large amounts of Mo, W and V, which are more carbide-forming elements than Fe represent. In addition, they have relatively good impact properties (notched impact strength), so that they usually primarily used as cutting tools

From the standpoint of the overall properties of steels such as wear resistance, heat resistance, pressure resistance and from the point of view of impact properties, high-speed steels are part of tool materials, e.g. Low temperature and high temperature cutting tools, superior

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and they are used as working tools for low temperature UEd high temperature operation in addition to cutting tools used.

In this case, however, it is important how the impact properties (Impact strength properties) can be improved can without impairing the wear resistance. For this purpose, a heat treatment, such as e.g. a low temperature curing applied. On the other hand, the suppression of the C content is beneficial for the improvement the impact properties from the viewpoint of the composition, however, this increases the wear resistance adversely affected.

The tests described below were therefore carried out, to develop tool steels that have both excellent wear resistance and excellent slack properties exhibit.

For this purpose, a typical example of a steel powder conforming to JIS SEI 9 (containing 0.5 % C, 4.3 % Cr, 5.1 % Mo, 6.0 % W and 2.0 % V) was used. Nitrogen was incorporated into this steel, and high-speed steels (high-speed turning steels) with various nitrogen contents were produced. In these high-speed steels, the influence of the nitrogen content on the wear resistance and the impact properties was investigated and the results shown in FIG. Ί were obtained.

As can be seen from the results shown in Fig. 1, when the nitrogen content is 0.40% or more, the wear resistance is markedly improved, and when the N content is less than 0.40 % , the impact strength is good, but it becomes apparently worse if the N content

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is more than 0.40 % .

Carbon, which is an essential element in high-speed steels generally has properties similar to those of nitrogen, which is an additional element (optional component) represent very similar. Each of these elements has a very small atomic number of 6 or 7 and is one atom of the interstitial Type that has a tendency to easily form an alloy compound. It therefore seemed pretty reasonable too be to adjust or regulate the nitrogen content in combination with the carbon content, for example under Reference to such factors as the (C + N) content or the C / N ratio, regardless of the C content. About that In addition, it is desirable to determine the nitrogen content with due consideration being given to the content of elements which are available to those skilled in the art are known as elements that work together with C and N in high speed steels can form carbides, such as in particular V, to regulate or adjust,

In view of the above, as will be explained in the examples below, steel powders conforming to JIS SKH 9 or 10, which are different from each other in terms of carbon content, were prepared, and nitrogen was added to these steel powders in an amount of at least 0.40 % incorporated, which was necessary to improve the wear resistance of the steels. Then, high-speed steels were manufactured from these powders by the powder metallurgy method, and they were tested for wear resistance and impact properties (impact strength), and the results obtained are shown in Figs.

Fig. 2 illustrates the results obtained with steels conforming to JIS SKH 9 »containing 1.95 to 2.04 % V. From the

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It can be seen from Fig. 2 that when the (C + N) content is more than 0.6 % , the wear resistance is markedly improved. On the other hand, when the (C + N) content is less than 0.9 % , the impact properties (notched impact strength) are good. In a nitrogen-containing high speed s-FM steel conforming to JIS SKH 9, the (C + N) content suitable for improving wear resistance without deteriorating impact properties (impact strength) is 0.6 up to 0.9%.

Fig. 3 explains the results, which are correspondingly in the case of steels JIS SKH 10 containing 4.45 "to 4.53% V. It can be seen from Fig. 3 that a suitable range for the (C + N) content is 1.1 to 1.4%.

FIG. 4 explains the results which are obtained with the steels raib with an increased V content, namely with 4 % Gr - 3.5% Mo - 10% V / 12 % V - steels ^. In this case, a suitable range for the (C + N) content is 2.6 to 2.9%.

Figure 5 also illustrates the results obtained on AISI A7 steels containing 4.78 to 4.83 % V and used in a cold working tool. In this case, a suitable range for the (C + N) content is 1.15 to 1.45%.

If the above experimental results obtained with various high speed s-PM steels are taken as a whole mainly with regard to the (C + N) and V contents are considered, it follows that to improve the impact properties (notched impact strength) without simultaneous Impairment of the wear resistance the following condition must be met:

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0.2 + 0.2 V (%) ^ (C + N) ^ C 0.5 + 0.2 V (%)

Under this condition, if the V content exceeds 15% , the toughness generally decreases drastically because a vanadium-type carbonitride is coarsened, and in such a case, the above relationship is a suitable range for the ( C + N) content that is suitable for the machinability, the heat treatment properties and the mechanical properties is not fulfilled.

However, if the vanadium content is more than 15 % , the grindability and forging properties are very much deteriorated because a vanadium-type carbonitride is coarsened. If the vanadium content is less than 1.6% , it becomes difficult in practice to enrich nitrogen in an amount of more than 0.4 %. The vanadium content must therefore be at least 1.6%. No substantial improvement in terms of workability is achieved if the nitrogen content is less than 0.40 % . According to the invention, the nitrogen content should preferably be at least 0.45 % .

As is apparent from the above experimental results, the above-mentioned relationship, namely, an appropriate range changes for the (C + N) content, in various high-speed steels, which differ in their content from such metals as Cr, Mo, Distinguish W and Co, do not.

* 'The present invention HI-V / He k zeugstähl en include tool steels, which are designated as alloy tool steels which contain relatively small amounts of Cr, Mo, W, Si, Mn and Ni with appropriate amounts of N, C and V, and this includes tool steels of a different type than

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High-speed steels (high-speed steels) are designated, which contain high amounts of these alloy elements, and this also includes tool steels, which contain medium amounts of these elements. Generally in tool steels the Cr is added in an amount of up to 15%, Mo is added in an amount of up to 10 % , W is added in an amount of up to 20 % and Co is added in an amount of up to 15% % added. In addition, up to 5% Ni, up to 1% Mn and up to 1% Si can be added as required. Furthermore, up to 2 % Zr, up to 5 % Nb, and up to 1% B can also be added.

The above-mentioned tool steels are widely used as metal molds such as a press tool, as Deburring nozzle, as a drawing nozzle and as a clamping device, e.g. as chisels, punches and gauges.

The invention is illustrated in more detail by the following examples, without, however, being restricted thereto.

example 1

Gas atomized Sbahlpuhrer according to JIS SKH 9, which relates to Differentiated from one another based on their carbon content, mild steel cans were filled, degassing and nitriding treatments and then compression molded using a hot isostatic press to perform heat treatment. The conditions of manufacture and the determination

»The wear resistance and impact properties (notched impact strength) The tests used are explained in more detail below.

2 · 2 conditions of manufacture

a) Chemical composition and grain size of the starting powder'-M.

The starting powders used are shown in the table below

I stated. * '709847/1179

b) nitriding treatment

The nitriding treatment was for 2 hours in a nitrogen atmosphere at 1150 ⁰ C. The pressure of the atmosphere was appropriately controlled to adjust the nitrogen content in the steel product.

c) Isostatic hot press treatment It was carried out for 2 hours.

It was hardened for 2 hours under 2000 atm at 1100 ° C

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Table I.

Kind of
use
ten steel Composition ^ C. Si Mn P. S. Cr Ko 6.12 V 0 N Grain size A.
(0.7 * C) 0.70 0.29 0.27 0.01 0.03 4.30 5.01 6.06 1.95 0.010 0.021 B.
(o.5Sic) 0.49 , 0.25 0.24 0.01 0.04 • 4.35 5.12 6.15 2.00 0.030 0.015 ^ 0.17 mm
(<8θ mesh) C.
(• O.3J6C)
I * 0.32 0.31 0.32 0.01 0.03 4.11 4.97 6.08 2.04 0.035 0.018 CO, 17 mm;
£ 80 mesh) D.
(0.1 # C) 0.11 0.32 0.29 0.01 0.02 4.05 4.91 2.01 0.040 0.017 <0.17 mm j
«80 mesh) i <v>,. ·; ^.
«SO mech];

d) heat treatment

Curing was carried out at 1150 ^{° C. for 5 minutes}

(oil check)

The annealing was 2 to 4 times repeated using a 1.5-hour heat treatment at 450 to 55O ⁰ C to

to achieve a hardness of HRC 59 to 60.

2.2 T ejst conditions

a) Wear resistance test Load: 4.5 kg Friction length: 550 m Friction speed: 2.5 m / Üek.

Material to be applied: JIS SCM 4 (QT), H _ß 300 Lubricant: none

b) impact test

R-notch 10mm Sharpy test

3 · Ο Te_sterresult £ 3e_

The test results are in the fi ^. 2 specified. As can be seen from the results shown in Fig. 2, in the nitrogen-containing high speed PM steels containing 2% V, the nitrogen content must be at least 0.4% in order to improve the wear resistance without impairing the impact properties (impact strength) suitable (C + N) content is 0.6 to 0.9 %. If the nitrogen content is less than 0.4%, the nitriding effect is insufficient. If the (C + N) content is less than 0.6 % * ~ , only a small amount of nitrite precipitation occurs and the wear resistance of the steel is impaired, while if it is more than 0.9 % , the impact strength is drastically reduced decreases.

With a nitrogen-containing cutting tool Hi-steel, as shown in Fig. 2, which contained 0.3% C and 0.4 % N,

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became an intermittent one with a cutting tool made from this steel Cutting test carried out.

Tool hardness: HRC 64 Tool shape: 0 °, 15 °, 6 °, 6 °, 15 °, 10 R Schnexde speed: 25 m / min.

Cutting depth: 1.5mm Feed speed: 0.2mm / revolution machined material: JIS SCM 4 (QT) H _ß 250 - 270

The cutting properties of this tool were confirmed to be equivalent to those of a cutting tool, that of a JIS SKH 9 high speed steel made by melting duration.

Example 2

Atomized steel powders conforming to JIS SKH 10 differing from each other in terms of their carbon content as shown in the following Table II were used as the starting powder, and high-speed PM steels containing nitrogen were made in the planar manner in Example 1 manufactured. The wear resistance and the notched impact strength were determined, and the results obtained are shown in FIG. ^{As can be seen} from the results shown in Fig. 3, a (C + N) content which effectively improves wear resistance without deteriorating impact strength is 1.1 to 1.4%. However, if the (C + N) content is within the range of 1.1 to 1.4 % , if the N content is about 0.3%, the improvement in wear resistance is insufficient as shown in Fig 3 shown.

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/ »6

φ.
η '* S5 G Λ
03 G n A. LL-,
: θ O O O W.
(U U
W. a 0 ti "G U O Q, OO
CJ O ο 00
CJ O ι s / / OO
v / CJ J W. rH tn ο O m ¹ ^ O -ο · CJ O
• σ
• ο
• O O ο in t-i O CJ in O
• O
• O
• O O O m CJ r-4 00 σ * O »Η • • • U in OO in in J « ^ * -3 " . * « Οι tn OO in . ) i-l OJ
il OI
1-I 1-I CJ r ~ hfl 5 CN 1-I O Ή « • M. • S ¹ ι- ¹
W. • rl
m \ - yJ2 o.o: O
«
O • i * *
O
•
O CO
Ö
αϊ U .02 .01 .02 I.
rf O ο O W. μ ι
Φ CJ in ON in lsi Ti Φ OW CJ Cl Cl O O O / ■ Ρ fH -PX! in rH CI <yy ί> · ΟΡ OJ KN. O O •
O rl
C \ ON
in rl
to O •
σ •
O O O * "* W. x °. CN VO m ^w c5 • CJ

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Example 3

Gas-atomized steel powders containing about 12 % V and differing in their carbon content as shown in Table III were used as the starting powder, and high-speed FM steels containing nitrogen were prepared therefrom in the manner shown in Example 1 . The wear resistance and the impact strength were determined, and the results obtained are shown in FIG.

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Table III

σ co

CU -4

Type of
use
deten
Steel Composition (2) C. Si Mn P. S. Cr Ho W. V 0 N Grain size H
(2.52c)
I.
(2.0 ^ C)
J
(1.72C) 2.50
2.01
1.69 0.29
0.29
0.35 0.31
0.30
0.30 0.01
0.01
0.02 0.02
0.02
0.03 4.01
4.04
4.09 3.56
3.61
3.75 10.3
9.8
10.4 12.2
12.3
11.8 0.041
0.030
0.050 0.18
(
0.18
(
0.15 <- 0.17 mm
^ 80 mesh)
CO, Ί7 mm
<^ 80 wesh)
<C, ^ 7 mn
(<80 mesh)

PO

ro

CD

«-A

As can be seen from the results shown in Fig. 4, a suitable (C + N) content which is effective in improving wear resistance without deteriorating impact strength is 2.6 to 2.9 % »

Example 4

Steel powder atomized by a gas according to AISI A 7 » as indicated in Table IV were used as the starting powder and this became nitrogen-containing high speed work s-FM steels produced in the manner indicated in Example 1. The wear resistance and impact strength were determined and the results obtained are in 5 shown.

■ '7 0 9 8 A 7/1 1 7 t

ZO

φ * "* 0 O * Α G ιη cq O ^Λ Ό ; ο νΟ 2 ο " ^e ο J ο IjO ο ο -ν / QO
CM
V νΟ j) ιη U O 00 ο ^α ρ VO O a ο O ό ο O , _, O -1· OC "^ ^- "F. O - • ί O *
O ιη
ο ο ό OO I ^ Γ » J O
« U VO 1-1 O O ο in ο ιη W. C ^ ¹ ^ C. Cl O O ιΗ O Cl ιη uD CU in tn OJ ο O -P ο " ο O Φ J · -. ό ιη W. ■ Η OJ > η (D OJ O ο C. O O ιη £ "- ' ό σ \ CD
ω CJ Oil • N •
ο ο U •
O ιη CQ I
O) pi η
-Ö (D flH ιΗ Oil Cl te (L) rU • ό -ρ η ρ rö ο O 3 * * CJ VO ο O ό νο " "^ O O

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The results shown in FIG. 5 show that that a (C + N) -content, which in an effective way the wear resistance improved without impairing the notched impact strength, is 1.15 to 1.4-5%.

Example 5

Two types of steel according to JIS SKH 9 »one relatively contained a small amount of nitrogen and by the powder metallurgy process or according to the Schraelz process (melting + Forging process), were based on the wear resistance and impact properties (Notched impact strength) tested. The chemical composition of these steels is given in Table V below.

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O I. > ο Ό U · I C O O ό • O O C O O O CO O! ri ri ι Ό £ -! I. C ^ CC i * · I ri O tO (Λ O O bO d ο *; 3 •H +3 W. ri ol
O O Φ •. W. O O £ 3 U ο · O CO
F ^ Cl CD
ta d ο η ISJ (U O ri (U tJ O O Cl 03 i-t Γ ~ ω «π te ^ J O O U cd Xi (U -P <h ι cd > W .0 ^ H-P C * ctia οω a .ρ Cj ö Cl C / 3 OT xj fn OT I .- O (U " CQ - W «Ö i2 (U £; ς (D (U C -C) U) N ^ -P 5S O

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The test results are given in Table VI below.

Table VI

steels used

N O

relative amount of wear notched impact strength (nmr / mkg) (mkg / m.)

2.2 10 2.1 χ 10

-3 -3

5.5 4.2

As a result, it was found that the impact strength of the Hi steel (N) was improved because the microstructure of the FM steel was uniform and fine compared to the microstructure of the molten steel (O), as from the ^ ig. 6a and 6b can be seen.

Example 6

Steel powder atomized by a gas according to JIS SKH 10, which contained 1.5 % C and 0.4 % N, was tested according to Example 1. The chemical composition is given in Table VII below and the test results obtained are given in Table VIII below.

Table VII

used steel

(P) N holding PM steel JIS SKH 10

Zusamme nsetzung (%) P

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Table VIII

used relative amount of wear notched impact strength ^steel (mmVmkg) (mkg / cm ² )

P 2.3 x 10 " ⁴ 0.53

As can be seen from Table VIII above, the wear and impact strength were the same as those of the steels containing 1.7% (C + N) according to FIG. 3. It should be noted that steels N, 0 and P outside lie within the scope of the present invention and are only given for comparison with the steels according to the invention are.

As is readily apparent from the above explanations, in the nitrogen-containing PM tool steel according to the invention achieves excellent wear resistance and excellent notched impact strength (impact properties) by adjusting and controlling the content of G, N and V so that the following conditions are met:

N £ 0.40%, preferably N ^ 0.4-5%, 1.6 = V ^ 15 % and 0.2 + 0.2 V (%), < (C + N) <0.5 + 0 , 2 V (%)

In addition, the steel according to the invention can contain at least one element selected from the group: up to 15% Cr, up to 10% Mo, up to 20 % W and up to 15% Co.

Furthermore, up to 3 % Ni, up to 1 % Mn and up to 1% Si can be incorporated into the steel according to the invention as required. The steel according to the invention can also contain up to 2% Zr, up to 5 % Nb and up to 1% B.

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Claims (4)

Claims 1. Nitrogen-containing powder metallurgy tool steel, characterized in that it contains: at least 0.40 % N, 1.6 to 15% V, C in an amount that satisfies the relationship: 0.2 + 0.2 V (%) ^ (C ₊ NK 0.5 + 0.2 V (%) at least one element selected from the group: up to 15% Cr, up to 10% Mo, up to 20 % W and up to 15 % Co, and the remainder iron. 2. Steel according to claim 1, characterized in that it contains at least 0.45 % N. 3. Steel according to claim 1 or 2, characterized in that it also contains at least one element which is selected becomes from the group: up to 3% Ni, up to 1% Mn and up to 1% Si. 4. Steel according to claims 1 to 3 »characterized in that it also contains at least one element which is selected from the group: up to 2% Zr, up to 5 % Nb and up to 1% B. 709847/1179 ORIGINAL INSPECTED